After a decade of false starts, Boeing pulled off an upset Thursday to win the $35 billion contract to build a fleet of Air Force aerial refueling tankers, a deal the company heralded as an economic boon of 50,000 jobs for Washington state and other parts of the country.

Deputy Defense Secretary William Lynn, who, along with the Pentagon’s acquisition chief and the top leaders of the Air Force, announced the decision, said the military’s third attempt to buy tankers was based on a number of criteria, primarily costs.

“Boeing was the clear winner of that process,” Lynn said.

And Washington state Rep. Norm Dicks, the ranking Democrat on the House Appropriations Committee, was ecstatic.

“This is one of the happiest days of my professional life,” he said, adding that a change he helped secure in the way the Air Force evaluated the price of the bids may have made the difference.

The Pentagon considered the cost of the planes over 40 years rather than 25 years, he said, and since Boeing’s NewGen Tanker will burn 24 percent less fuel than the EADS A330 plane, Boeing had a new edge.

“The life cycle cost, I think, was decisive,” Dicks said. “It’s a great victory.”

The decision was 10 years in the making, after bitter back-and-forth lobbying, advertising and scandal. Two earlier efforts foundered, with one ending the careers of several Air Force officials and landing a Boeing executive in jail and another award to the European Aeronautic Defence and Space Co. and Northrop Grumman in 2008 being overturned after Boeing protested.

The world’s two largest aerospace companies — EADS and Boeing — are used to operating in such a cutthroat environment. But the regions and politicians competing for tanker business also have good reason to fight so hard: The contract is good news for a nation racked by high unemployment. EADS, the parent company of Airbus, plans to assemble its tankers in Mobile, Ala., a state that doesn’t rely on union labor; Boeing would build its tanker in Everett, Wash.

“This is a spark that can turn the economy in another direction. This is a lot of work for many, many, many years,” said Rich Michalski, general vice president of the International Machinists and Aerospace Workers Association, a union that backed Boeing in the spirited competition. “This is $4 billion of generated income for American workers per year.”

The Pentagon is expected to provide both companies with detailed briefings soon. And members of Congress are expected to receive the full explanation next week, congressional and industry sources said.

News of the Pentagon’s decision first trickled out of the Washington state congressional delegation, followed shortly after the official announcement with a barrage of triumphant statements.

“At a time when our economy is hurting and good-paying aerospace jobs are critical to our recovery, this decision is great news for the skilled workers of Everett and the thousands of suppliers across the country who will help build this critical tanker for our Air Force,” said Sen. Patty Murray (D-Wash.). “This decision is a major victory for the American workers, the American aerospace industry and America’s military. And it is consistent with the president’s own call to ‘out-innovate’ and ‘out-build’ the rest of the world.”

On the other side, Rep. Jo Bonner (R-Ala.) said he’ll demand a full explanation of the bidding process. “This competition has been challenged before, and it’s not unlikely it will be challenged again,” Bonner said. “It will ultimately be up to EADS to determine whether they will protest this decision, and I will fully support whatever decision they make.”

The Air Force has made a cogent enough case for its decision that EADS won’t have grounds for a protest, Lynn told reporters.

EADS did not immediately indicate whether it would move to overturn the award.

“This is certainly a disappointing turn of events, and we look forward to discussing with the Air Force how it arrived at this conclusion,” said EADS North America Chairman Ralph Crosby.

For Boeing, it was a time to celebrate the ability to continue producing tankers for the Air Force; it made the current fleet of KC-135 aircraft developed in the Eisenhower era.

“We’re honored to be given the opportunity to build the Air Force’s next tanker and provide a vital capability to the men and women of our armed forces,” said Boeing’s chairman, president and CEO, Jim McNerney. “Our team is ready now to apply our 60 years of tanker experience to develop and build an airplane that will serve the nation for decades to come.”

Before Thursday’s announcement, EADS had been the favorite — largely because of a story line driven by Loren Thompson, chief operating officer of the Lexington Institute, who was the first to predict Boeing would lose. Thompson, who’s been far from neutral on the issue, has clearly favored Boeing.

But others saw EADS talking openly about discounts and Boeing’s supporters grumbling more and more.

In this, the third time the Pentagon has tried to bid the fleet of 179 aerial tankers, Boeing’s surrogates took a defensive posture and appealed to the White House for help in steering the contract to Boeing, with lawmakers and governors from Washington state and Kansas leading the charge.

But the White House said it was staying out of the procurement business. And chief of staff Bill Daley recused himself, since he had been on the board of Boeing, headquartered in his hometown of Chicago.

Boeing’s backers have argued since Northrop Grumman, the old partner of EADS, dropped out in March that EADS should not receive additional time to recast its bid. But the Defense Department granted an extension, keeping EADS in the running.

The extension also enabled a Russian company to put together its own bid, but the company’s deliveryman got lost on his way through Wright Patterson Air Force Base in Ohio and showed up minutes late, allowing the military to turn away the proposal.

EADS suffered a setback last summer, when EADS North America CEO Sean O’Keefe was injured in the plane crash that killed former Sen. Ted Stevens (R-Alaska).

And in November, the Air Force mistakenly sent computer disks to the two contractors containing information about their competitor’s score on a computer model vital to the contract award, opening up a new avenue of discontent. After the mix-up, the Air Force shared the data with both companies.

Throughout the competition and previous rounds, Boeing and its supporters have argued that the EADS bid should be docked because of an ongoing World Trade Organization dispute involving illegal subsidies.

EADS had been cautiously optimistic about its bid for weeks and had focused primarily on the nuts and bolts of the competition, while taking a few shots at Boeing.

“My take is: The rules are clear in terms of the requirements, the pricing methodology and the evaluation criteria. So our perspective is, we’re in this game, a game well-defined, a game we intend to win,” Crosby told reporters after announcing EADS had lowered its price to be more competitive.

Asked how much the price had dropped, Crosby quipped, “Just enough to win.”